Micron-sized mechanical structures cofabricated with electrical devices or circuitry using conventional Integrated Circuit (IC) methodologies are called micro-electromechanical systems or MEMS. There has been a great deal of recent interest in the development of MEMS devices for applications such as projection devices, displays, sensors and data storage devices. For example, one of IBM's projects concerning data storage device demonstrates a data density of a trillion bits per square inch, 20 times higher than the densest magnetic storage currently available. The device uses thousands of nanometer-sharp tips to punch indentations representing individual bits into a thin plastic film. The result is akin to a nanotech version of the data processing ‘punch card’ developed more than 110 years ago, but with two crucial differences: the used technology is re-writeable (meaning it can be used over and over again), and may be able to store more than 3 billion bits of data in the space occupied by just one hole in a standard punch card.
The core of the device is a two-dimensional array of v-shaped silicon cantilevers that are 0.5 micrometers thick and 70 micrometers long. At the end of each cantilever is a downward-pointing tip less than 2 micrometers long. The current experimental setup contains a 3 mm by 3 mm array of 1,024 (32×32) cantilevers, which are created by silicon surface micro-machining. A sophisticated design ensures accurate leveling of the tip array with respect to the storage medium and dampens vibrations and external impulses. Time-multiplexed electronics, similar to that used in DRAM chips, address each tip individually for parallel operation. Electromagnetic actuation precisely moves the storage medium beneath the array in both the x- and y-directions, enabling each tip to read and write within its own storage field of 100 micrometers on a side. The short distances to be covered help ensure low power consumption.
FIG. 1 is a partial cross section view of such device (100). As shown, each cantilever 115 is mounted on a substrate 105 surmounted by a CMOS device 110, with a control structure 120, and comprises a downward-pointing tip 125 that is adapted to read or write (R/W) a bit on the surface of the storage scanner table 130. Thanks to electromagnetic actuator 135 storage scanner table 130 can move in at least one dimension as illustrated by arrows. The part comprising the storage scanner table 130, the actuator 135 and the support structure 140 must be precisely aligned on the CMOS device 110, at a predetermined distance. CMOS device 110 has all the required electronics to control required functions such as R/W operations. In this implementation example, alignment functional targets in X and Y axis are on the order of ±10 μm (micrometer), while the functional gap between the storage scanner table 150 and the CMOS device 110 that works also as a supporting plate for the R/W cantilevers has a maximum distance of 6 μm with sub-micron tolerance.
The combination of electrical and mechanical features associated with the required part alignment accuracy leads to the use of dedicated manufacturing tools that directly impacts device cost. In the high volume production of this kind of product for the consumer market such investments would become very high due to an intrinsic conflict between throughput (capacity) and precision alignment requirements. Therefore, there is a need for a method and systems for aligning efficiently parts of the MEMS during manufacturing, without requiring dedicated and complex manufacturing tools.